This invention relates to an intraocular lens and, more particularly, to an intraocular lens that can be surgically implanted in an eye through a very small incision. The invention also relates to a method of surgically implanting such a lens.
In the human eye, the natural lens is situated behind the pupil and iris, and it serves to focus light entering through the cornea and pupil onto the retina at the rear of the eye. The natural lens comprises a biconvex crystalline structure, normally highly transparent, and a lens capsule surrounding the crystalline structure. The lens is supported at its outer periphery by suspensory ligaments, called zonules, that are connected between the lens capsule and the surrounding ciliary muscle.
A cataract condition is present when the material within the lens capsule becomes cloudy, as a result, for example, of age, trauma, or some metabolic problem. As the lens clouds, light passing through it is reduced, and vision becomes progressively blurrier as this clouding increases.
Technology and methods exist today that enable a surgeon to remove the clouded natural lens, or cataract, through a relatively small incision 3 or 4 millimeters (mm) or less made near the periphery of the cornea. In small-incision extra-capsular cataract extraction, the surgeon enters the eye through this small incision, makes an opening through the front wall, or anterior capsule, of the lens, and then removes the clouded cellular material through this opening and the small incision. Various techniques are available for effecting such removal, one of which is called phaco-emulsification. This involves ultrasonic fragmentation of the nucleus of the cataract into small particles and removal of such particles by suction, all of which is effected through a slender, hollow phaco-emulsification tip inserted through the small incision. The remainder of the cataractous material is removed through use of a slender irrigation and aspiration tip also inserted through the small incision; and when this removal step is completed, there is left a clean lens capsule free from cataractous material.
The next step in this surgical procedure is to introduce an artificial lens into the space formerly occupied by the crystalline portion of the natural lens. The vast majority of intraocular lens implants used today have a lens body composed of a rigid material with a diameter of 6 mm or more. Insertion of such an implant requires enlargement of the 3 or 4 mm small incision to allow for entry of the implant, thus defeating many of the advantages of the small incision. Among these advantages are more rapid healing, less astigmatic induction, less deformation of the shape of the globe, and more rapid restoration of the patient to active life with less post-operative discomfort.
Numerous proposals have been made to provide intraocular implants that can be inserted and positioned through the above-described small incision. For example, there are available foldable implants that are inserted in a folded condition through the incision and then unfolded while in the eye. These foldable implants are cumbersome to insert and position, oftentimes requiring use of an inserter instrument that can gape the wound or that may necessitate enlargement of the wound to accommodate the inserter instrument along with the implant.
Another available type of implant, an example of which is disclosed in U.S. Pat. No. 4,556,998--Siepser, is one made from a solid hydrophilic material that is hydrated by fluid in the eye, causing it to expand after implantation. Before such expansion, it is small enough to fit through the small incision. A problem with this type of implant is that there is a large degree of variability and unpredictability in the expansion dimensions of the implant, thus causing problems with centering and positioning the implant.
Still another approach to the basic problem of inserting the implant through a very small incision is to make the lens from a plurality of parts which are subsequently assembled together within the eye. Examples of this approach are disclosed in U.S. Pat. Nos. 4,636,210--Hoffer, 4,451,938--Kelman and 4,573,998--Mazzocco. This approach usually requires complicated and awkward means for holding together the parts of the final assembly and for positioning the final assembly or requires for assembling the parts awkward procedures involving the use of surgical tools within the eye, thus increasing the risk of accidental injury to the cornea, iris, or lens capsule.